Lawmaker discloses portion of intelligence study that concludes Pyongyang has the technology to make warheads small enough for long-range missiles. It is not a view shared by all U.S. spy agencies.

WASHINGTON -- A U.S. intelligence agency has concluded that North Korea has the capability to develop nuclear warheads small enough to fit on a ballistic missile, a congressman disclosed Thursday.

Although U.S. experts believe that North Korea cannot hit the U.S. mainland with its missiles, a significant improvement in Pyongyang's weapons technology would be deeply disconcerting for U.S. policymakers. It would also help explain American measures -- including an emphasis on the U.S. ability to respond with nuclear weapons -- after weeks of warlike rhetoric from Pyongyang.

Regional intelligence officials and analysts say North Korea is poised to launch as many as five missiles from its east coast, but that they did not appear to be in preparation for war. They said the launches were likely to only be part of a military exercise and would not pose a threat to the United States or its allies, Japan and South Korea.

Analysts said the exercise would probably be part of festivities planned to mark the birthday Monday of the country's late founder, Kim Il Sung, grandfather of the current leader.

At a House Armed Services Committee hearing focused on the budget, Rep. Doug Lamborn (R-Colo.) read from what he said was an unclassified portion of a classified Defense Intelligence Agency study. "DIA assesses with moderate confidence the North currently has nuclear weapons capable of delivery by ballistic missiles. However, the reliability will be low," it says.

Lamborn said the DIA study was completed last month, but that the conclusion had not been made public.

Pentagon spokesman George Little said he could not address the details of a classified report. However, he added, "It would be inaccurate to suggest that the North Korean regime has fully tested, developed, or demonstrated the kinds of nuclear capabilities referenced in the passage."

James Clapper, the director of national intelligence, said in a statement that the DIA view is not a formal assessment shared by all U.S. intelligence agencies.

The DIA tends to be more aggressive in its intelligence assessments than the CIA, according to Bruce Klingner, a former CIA analyst on North Korea. He said the DIA has hinted in the past that Pyongyang could mount warheads on its missiles.

The Pentagon announced last month that it plans to augment missile defense systems in Alaska in response to the North Korean threat. The Defense Department also said it will deploy another antimissile system to Guam, which is within range of North Korean missiles.

The Pentagon also sent two long-range B-2 bombers from their base in Missouri last month on a round-trip flight to South Korea as part of a military exercise.

North Korea claimed after its most recent nuclear test in February that its objective was to develop a smaller and lighter warhead with "diverse materials."

Analysts said the statement indicated that Pyongyang was stepping up its development of a miniaturized warhead that could fit atop one of its long-range missiles, and that the device used enriched uranium as a trigger, rather than the plutonium previously used.

North Korea's official news agency said the nuclear test was successful. Seismic monitoring systems measured a resulting earthquake of magnitude 5.1, slightly higher than in past tests. But U.S. officials said yield estimates were uncertain.

At a Pentagon news conference last month to announce expansion of the U.S. missile defense systems, Defense Secretary Chuck Hagel did not answer directly when he was asked when North Korea would have intercontinental ballistic missiles armed with nuclear warheads. He said the U.S. goal was to stay ahead of the development of North Korea's weapons.

David Albright, a nuclear weapons expert with the Institute for Science and International Security, said in February that he believed North Korea has had the capability to mount a plutonium-based warhead on its shorter-range Rodong missiles "for some time," and was making progress on developing a warhead for an intercontinental ballistic missile.

He said that the U.S. intelligence community has not "been of one opinion" on North Korea's ability to produce miniaturized warheads. "Key members" of the intelligence community have credited Pyongyang with the ability to produce smaller warheads "for many years," he said but that conclusion was based on assessment and "not concrete evidence."

At a different congressional hearing Thursday, Clapper sought to downplay the recent tensions with North Korea. He said tensions were worse in previous episodes in his career, but he underscored how uncertain the intelligence is about North Korea's new leader, Kim Jong Un.

"We don't have good detail on the inner sanctum," he said. "There's no telling how he's going to behave. He impresses me as impetuous, [and] not as inhibited as his father became about taking aggressive action."